Basic Concepts in Immunity Antibodies Protein substances or Globulins derived from B and T lymphocytes Formed by the body as a defensive response Titers (concentrations) can be measured to specific antigens Antigen Foreign substance or seen by the body as foreign Stimulates antibody production

Host Defense Mechanisms Active Immunity (natural and artificial) Body produces antibodies in reaction to antigen (e.g. natural~acquired, and artificial~vaccinations) Typically takes 2-3 weeks to confer immunity Passive Immunity (natural and artificial) “borrowed” in 3 ways: Injection of serum with antibodies produced by another host (e.g., immunoglobulin) Placental transfer (short-term immunity) Breastfeeding Immunity is immediate

Herd Immunity Resistance of group or population to spread of specific disease through group Resistance due to high proportion of population immune to disease (usually due to previous immunization or infection) Theoretically, when 85-90% of population is immune, herd immunity should protect other 10- 15% However localized outbreak could occur if not well distributed http://www.health.harvard.edu/video/herd-immunity/

Source: JHSPH Open CourseWare. Fundamentals of Epidemiology

Carrier of Communicable Disease Harbors infectious agent Asymptomatic No overt signs or symptoms Can be transmitted to others Can be carriers during incubation period or for long periods of time (chronic carriers) “Typhoid Mary” http://www.youtube.com/watch?v=w0dYpUjr-Cg Typhoid Mary – In the early 1900’s, Mary Mallon was a cook for a family in Long Island. 5 living in house contracted typhoid fever. Family commissioned George Soper, sanitary engineer from NYC Heatlh Dept. He suspected Mary who disappeared to NYC even though she had no S&S. She threatened him when he wanted to test her for disease. He looked into her work history and found that 7 of 8 families for whom she had worked contracted the disease. A 1903 epidemic in Ithaca which infected 1300 people was thought to have originated with Mary. She was teken kicking and screaming to be tested in NY. Although she had no visible S&S, she was found to have the bacteria that caused typhoid fever in her feces. She was given option to remove gallbladder to end carrier state, but she refused. They sent her to an isolation cottage on N. Brother Island in NY. She was released after 3 years due to public outcry. Conditions of her release included staying in contact with public health officials and not working in food handling profession. She changed her name and was found several years later working as cook in Maternity hospital in NYC where several more cases were attributed to her. She was arrested and taken back to the isolation cottage for the remainder of her life. She lived to be 70 years of age. Sometimes can’t only look for people with obvious S&S of disease

Vaccination Active immunity produced by vaccine Immunity and immunologic memory similar to natural infection but without risk of disease

Classification of Vaccines Live attenuated viral bacterial Inactivated

Whole Fractional Inactivated Vaccines viruses bacteria protein-based toxoid subunit polysaccharide-based pure conjugate Fractional

Principles of Vaccination General Rule The more similar a vaccine is to the disease-causing form of the organism, the better the immune response to the vaccine

Live Attenuated Vaccines Attenuated (weakened) form of the "wild" virus or bacterium Must replicate to be effective Immune response similar to natural infection Usually produce immunity with one dose* *except those administered orally

Live Attenuated Vaccines Severe reactions possible Interference from circulating antibody Fragile – must be stored and handled carefully

Live Attenuated Vaccines Viral measles, mumps, rubella, varicella/zoster, yellow fever, rotavirus, intranasal influenza, rotavirus, vaccinia Bacterial BCG, oral typhoid

Inactivated Vaccines Cannot replicate Generally not as effective as live vaccines Less interference from circulating antibody than live vaccines Generally require 3-5 doses Immune response mostly humoral Antibody titer may diminish with time

Whole-cell vaccines Inactivated Vaccines Viral polio, hepatitis A, rabies, influenza* Bacterial pertussis*, typhoid* cholera*, plague* Whole-cell vaccines *not available in the United States

Fractional vaccines Inactivated Vaccines Subunit hepatitis B, influenza, acellular pertussis, human papillomavirus, anthrax Toxoid diphtheria, tetanus Fractional vaccines